1. Field of the Invention
The invention relates to a fuel injection control apparatus and a fuel injection control method for a compression ignition internal combustion engine.
2. Description of the Related Art
Japanese Patent Application Publication No. 60-017250 (JP-A-60-017250), Japanese Patent Application Publication No. 2001-193463 (JP-A-2001-193463), Japanese Patent Application Publication No. 2004-027939 (JP-A-2004-027939), Japanese Patent Application Publication No. 2006-274969 (JP-A-2006-274969), and Japanese Patent Application Publication No. 11-93735 (JP-A-11-93735) describe a fuel injection control apparatus for a compression ignition internal combustion engine such as a diesel engine, which injects high pressure fuel stored in a common rail a plurality of times into each cylinder during one combustion stroke.
In this kind of a diesel engine, only a small amount of fuel is injected when the engine is operating in the low load region so the temperature in the cylinders tends to fall. If the temperature in the cylinders (hereinafter also referred to as “cylinder temperature”) falls, combustion may become unstable, leading to an increase in the amount of hydrocarbons (HC) that are produced. One way to minimize the amount of HC produced is to inhibit the cylinder temperature from dropping by performing a pilot injection by which a small amount of fuel is injected ahead of the main injection. Also, performing a pilot injection over a series of injections (i.e., performing a plurality of pilot injections before one main injection) enables a drop in the cylinder temperature to be effectively suppressed.
However, when such a pilot injection is performed right after a fuel cut is executed, for example, torque shock may be produced when the operating region of the engine shifts from the low load region to the fuel cut region or from the fuel cut region to the low load region depending on the number of pilot injections, and this torque shock may adversely affect drivability.